This invention relates to a construction preform for use in forming an archway in walls or door frames. In particular, the preform is affixed directly to the wall support members so as to provide a base for the wallboard or drywall used on the adjacent wall.
The construction of an archway has normally required the assembly of a wooden support at the construction site. Plywood is cut in a manner to provide the outline of the arch when completed. Two sections of plywood are separated by spacers which maintain the relative position of the two sections of plywood during affixation to the adjacent studs and headers defining the unfinished opening. After affixation of the curved plywood form, it has been common practice to affix strips of drywall to support pieces serving as spacers. Since the objective is to form a continuously curved surface along the exposed face of the intermediate supports, the use of thin strips of drywall to form the exposed surface of the archway is made to approximate a curve. The process of affixation of the drywall strips is time consuming. Attempts to cut wider strips to shorten construction time is limited by the desired contour. In order to finish the irregular approximation of the desired arch curve, the use of a drywall compound in substantial thickness is normally required. The construction process can result in a nonsymmetrical arch if great care is not taken.
In an attempt to overcome problems associated with the fabrication of an archway at the jobsite from the combination of contoured plywood, drywall and the intermediate support strips, prefabricated archways made from molded foamed plastics have been used. A prefabricated archway formed of molded polyethylene is described in U.S. Pat. No. 4,601,138 to Hampton wherein a relatively light weight arch can be brought to the location of the project and nailed or otherwise affixed directly to the framing of the adjacent wall. The prefabricated plastic archway is dimensioned to be conformably received in abutting relationship to the adjacent edges of the wall surfaces. The width from one outer surface to the opposing outer surface of the prefabricated archway is equal to the distance between the finished surfaces of the opposing walls. In other words, the arches are dimensioned to form a butt-joint against the existing drywall or wallboard. The prefabricated archway is secured in place by a series of nails applied through the exposed surface of the foam into the studs and headers comprising the support members. Following affixation, conventional taping is applied to the seam between foam and adjacent drywall. In practice, the seam between adjacent drywall and the foam arch has been found to display cracking due in part to the use of dissimilar materials at the seam thereby requiring future repair and maintenance. Also, the subsequent movement of nailheads outwardly and away from the foam archway creates an unsightly appearance requiring further maintenance.
The problems mentioned above in connection with prefabricated archways formed of foamed plastic is addressed in U.S. Pat. No. 4,665,666 to Hampton wherein the use of drywall paper in the molding process is recommended. During the formation of the archway, the reference teaches lining the mold with drywall paper which then becomes permanently bonded to the molded archway. As noted in the patent, the drywall paper strengthens the finished arch by adding a fibrous laminate to its exterior surface so as to reduce cracking. Furthermore, the use of the paper is intended to eliminate the "nail pops" occurring after installation. This modification to the construction of prefabricated archways is required because of the incompatibility of foamed plastic material with the wall-defining materials used in normal construction techniques. While the molded foam prefabricated archways accomplish the goal of eliminating the construction of coarse archway forms at the construction site, the problems arising from the use of a foamed material such as seam parting, cracking, nail popping and limited resistance to applied pressure remain.
Accordingly, it is a primary objective of the present invention to provide a durable archway preform which is complete when delivered to the construction site. In addition, an objective of the present invention is to provide a preform which allows the adjacent wall material to cover both the preform and adjacent wall surface in a continuous manner thereby eliminating seam parting or cracking. Also, the invention provides a preform which can receive threaded fastening devices thereby eliminating the maintenance problems associated with nails moving from their original position and causing unsightly surface damage.